Thermal fill bonding method

ABSTRACT

A Thermal Bonding Method and Apparatus to thermally bond sheets of fill in a cooling tower fill pack. The apparatus creates a hemispherical joint extending through two fill sheets to provide a substantial joint between said sheets.

FIELD OF THE INVENTION

This invention relates to methods and apparatuses for bonding fillsheets.

BACKGROUND OF THE INVENTION

It is well known that film-type cooling tower fill packs are strongerand easier to install when the sheets are bonded together well. Somefill sheet bonding techniques include chemical welding, snap buttons,rods, screws, nails, and thermal bonding. Chemical welding is the mostcommon and is also usually the strongest, but requires the use ofsolvents and a flash time for the bond to set. Chemical welding isusually performed at a different location from the installation due torestrictions on solvents and the extreme amount of time necessary toallow the pack to cure. Snap buttons can be used at the installationsite, but the joints are easily detached. Rods, screws, and nailsrequire additional parts to be added to the pack, which increases cost.These joints are also not as substantial as chemical welding. Thermalbonding has, until this invention, been difficult to achieve asatisfactory bond. Existing methods also have difficulty reaching theinterior bond sites in the pack, leading to a weak pack. This inventionovercomes the current limitations for on-site bonding as well asproducing a factory bond that eliminates the need for solvents.

SUMMARY OF THE INVENTION

The method presented herein distinguishes itself from other methods byallowing multiple sheets to be stack-bonded without any backing behindthe sheet. This is accomplished through the implementation of aninsulating bushing that holds the sheets down while the bond site ismelted, plus an air pulse that forces the sheets together when the tipis retracted. Existing processes can only completely bond two sheets ata time. These two sheet assemblies are then attached to each other onlyby the edges. Our invention provides a full field of bonding sites toevery sheet in the stack.

According to an embodiment of the invention, a thermal bonding device isused thermally weld fill sheets together. A special bonding tip designprovides a method and apparatus to create a hemispherical bond thatunites two fill sheets together without the need of a backing die,allowing the fill pack to be created in any thickness while reachingeach and every bond site within the pack.

Accordingly, there is provided according to the invention, a thermalbonding method having the steps:

-   -   a. placing alternating film fill sheets on a stack;    -   b. heating a hemispherical bonding tip to the melting point of        the fill sheet;    -   c. plunging the bonding tip vertically onto a bond site on the        fill sheet until the spring is compressed;    -   d. waiting a specified amount of time for the tip to melt into        the fill sheet down to the insulating bushing;    -   e. the insulating bushing providing a positive stop to position        the bond tip;    -   f. providing a pulse of air through the bonding tip that pushes        the melted sheets together; and    -   g. removing the bonding tip from the joint so the bond can cool.

Different fill sheet thicknesses, environmental temperature, and plasticchange the melting time. According to a preferred embodiment, a melttime of 5-10 seconds may be used on 10 mil PVC at 65°-85° F. airtemperature.

The method may be carried out with specific durations for each step, andsome steps can occur simultaneously. According to one embodiment, thesteps of placing, heating, and plunging all happen at the same time.Additionally, the air pulsing step may happen at the same time asremoval. The method may be carried out with specific pressure andduration of air through the tip that may “bubble-out” the bond site. Thepressure and duration of air depends on the material thickness, type ofplastic, and ambient temperature. According to one embodiment, 60 psimay be applied to the air manifolds and the pressure at the bond sitevaries from 1-20 psi for about 1 second.

According to another embodiment of the invention, there may be provideda thermal bonding device having:

-   -   a. a hemispherical bonding tip extending through an insulating        bushing;    -   b. a heater block to provide the temperature necessary to heat        the bonding tip to a level near the melting point of the fill        sheet;    -   c. a spring mechanism attached to the bonding tip to provide a        resistance force;    -   d. a sliding mechanism allowing the bonding tip to move        vertically; and    -   e. an air conduit to provide a pulse of air to the bond zone;

According to further embodiments, the device may have a ship's hullshaped tip. According to further embodiments, the device may be providedwith a weight to provide resistance to the bond tip. And according tofurther embodiments, the device may be provided with differentinsulating bushing shapes. According to one embodiment, the bushing maybe ⅜″ outside diameter with a ¼″ inside diameter. The bushing may bechanged from the illustrated “pipe” shape to an elliptical shape toprovide more insulator surface area in odd shaped fill geometries.

The invention may be used with all plastic fill materials and with bothcounterflow and crossflow fill designs.

DESCRIPTION OF THE DRAWINGS

The subsequent description of the preferred embodiments of the presentinvention refers to the attached drawings, wherein:

FIG. 1 is a schematic showing the major components of a fill bondingapparatus according to an embodiment of the invention.

FIG. 2 shows a cross-sectional view of the thermal bonding tip accordingto an embodiment of the invention.

FIG. 3 shows an outside perspective view of the thermal bonding tipaccording to an embodiment of the invention.

FIGS. 4a through 4i show the sequence of operation for placing fillsheets and creating the bond according to an embodiment of theinvention.

FIGS. 5a through 5e show the sequence of operation for the bonding tipaccording to an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows the major components of the fill bonding apparatus. Twodifferent sheet types, Type A and Type B, are loaded onto feeder trays 1and 2, respectively. Gantry 3 moves horizontally to pick and placesheets type A and B, alternately, on the fill stack 4. Vacuum chucks 5and 6 remove the sheets from the stacks 1 and 2. Arrays of thermalbonding tips 7 weld the sheets together when they are placed on the fillstack 4.

FIG. 2 illustrates the main parts of the thermal bonding device.Hemispherical tip 10 extends through insulator and holding bushing 20.Heater block 30 provides heat to the tip 10. Air passage 40 extendsthrough heater block 30 and rod 50 to provide a conduit for pressurizedair to the tip 10. Rod 50 extends vertically through slide bushing 60 toallow vertical movement of the heater block, tip, and rod. Spring 70provides vertical force resistance to movement of tip 10. Collar 80 isfixed to tip 10 and provides a positive vertical stop to the motion ofthe tip. Heat sensing device 90 provides feedback to control thetemperature of the tip 10.

FIG. 3 illustrates an isometric view of the thermal bonding apparatus.

FIG. 4a is an elevation view of the fill bonding apparatus illustratingthe starting position in the sequence of operation with parts labeled asin FIG. 1.

FIG. 4b illustrates simultaneously raising the stacking tray 4 and thesheet type A feeder tray 1. Sheet type A is loaded into the gantry 3 andheld in place by the vacuum chuck 5.

FIG. 4c illustrates simultaneously lowering the sheet type A feeder tray1 and stacking tray 4 while sheet type A is in the loaded position.

FIG. 4d illustrates moving the gantry 3 to the sheet type B loadingposition and sheet type A stack placing position.

FIG. 4e illustrates simultaneously raising the stacking tray 4 and sheettype B feeder tray 2. Sheet type B is loaded into the gantry 3 and heldin place by the vacuum chuck 5. Sheet type A is released by the vacuumchuck and placed on the stacking tray 4.

FIG. 4f illustrates simultaneously lowering the sheet type B feeder tray2 and stacking tray 4 while sheet type B is in the loaded position.

FIG. 4g illustrates moving the gantry 3 to the sheet type A bondingposition and sheet type B stack placing position

FIG. 4h illustrates simultaneously raising the stacking tray 4 and sheettype A feeder tray 1. Sheet type A is loaded into the gantry 3 and heldin place by the vacuum chuck 5. Sheet type A and sheet type B are bondedtogether on the stacking tray 4. This is the same position shown in FIG.4b except bonding is being performed.

FIG. 4i illustrates returning the sheet type A feeder and stacking trayto the start position as illustrated in FIG. 4c which shows the gantry 3loaded with sheet type A.

FIG. 5a illustrates the bonding tip just contacting the fill stack asthe fill stack moves up. The bond tip heated. This occurs in position 8of the machine.

FIG. 5b illustrates the bonding tip being pushed up as the fill stackcontinues to move up. This compresses the spring and puts downwardpressure on the bonding tip

FIG. 5c illustrates the heated bonding tip extending down into the fillstack bond point as the sheets are heated. The spring decompressespartially during this step as the tip “melts” down into the bond site,still keeping pressure on the bond. The holding bushing 20 prevents thebonding tip from pushing too far into the fill stack.

FIG. 5d illustrates the end of the bond heating cycle. At this point,the bond is melted together. As the fill stack is lowered, a burst ofair is injected through the tip which pushes the sheets together andimproves the bond strength. This air burst also helps eject the tip fromthe bond site without sticking. A “bubbled-out” joint can also beprovided to enhance the bond, in which the melted bond site is blowninto a partial bubble shape as air is injected. The bubble is a largeron the bottom of the joint, which keeps it from pulling out. Someinstantaneous cooling may also occur, solidifying the joint.

FIG. 5e is the last step and corresponds to position 1 of the machinecycle. The tip has been completely removed from the bond site, and thesite is allowed to cool.

1. (canceled)
 2. (canceled)
 3. (canceled)
 4. A thermal bonding devicecomprising: a hemispherical bonding tip extending through an insulatingbushing; a heater block to provide a temperature sufficient to heat thebonding tip to a melting point of a film fill sheet; a spring mechanismattached to the bonding tip to provide a resistance force; a slidingmechanism allowing the bonding tip to move vertically; and an airconduit having an outlet on a contact surface of said bonding tip toprovide a pulse of air to a bond zone of the film fill sheet.
 5. Thedevice of claim 4 further comprising a ship's hull shaped tip.
 6. Thedevice of claim 4 further comprising a weight to provide resistance tothe bond tip.
 7. The device of claim 4 comprising a non-cylindricalinsulating bushing shape.